Kinetic Energy Measurements of Fragment Ions with a Time-of-Flight Mass Spectrometer.

A new apparatus for kinetic energy measurements of fragment ions has been developed. This apparatus is based on a time-of-flight (TOF) mass spectrometer with a pulsed electron gun. We can distinguish between thermal ions and energetic ions on a TOF spectrum obtained from this apparatus, using the time-lag defined by the time between the ionization and the application of the extracting pulse. During this time-lag, since energetic ions are dispersed from the ionization region, we can't detect the energetic ions except ones that move in the direction of the detector. On the other hand, since the thermal ions move little, all of thermal ions can be detected. The kinetic energy distributions of fragment ions were calculated by considering the collection efficiency of ions. The performance of our new technique is evaluated by the comparison between our experimental data of kinetic energy distributions of the protons dissociated from a methane molecule and those of the previous works.